Background: Despite ongoing efforts to mitigate air pollution, the complex relationship between pollution and climate change presents additional multifaceted challenges. Rising temperatures intensify air pollution issues by increasing ozone formation and wildfire-generated particulate matter release, yet understanding the co-occurrence of extreme temperatures and air pollution remains limited. Moreover, previous definitions of extreme temperature events have often overlooked regional vulnerabilities, influenced by different socioeconomic factors, population demographics, and climate adaptation measures.

Method: we analysed the spatiotemporal distribution of extreme risk-temperature (ERT) days and their interplay with air pollution exceeding WHO guidelines across 1426 NUTS3 regions in Europe During 2003-2020. The heat and cold risk thresholds are derived by epidemiological models based on mortality data from 35 European countries. Daily ambient PM2.5, PM10, NO2, and O3 concentrations were estimated at a 0.1-degree resolution.

Results: we observed that Europe's heat-ERT days increased from 13.76 to 17.09 days per year between 2003-2011 and 2012-2020, while cold-ERT days decreased from 20.69 to 12.94 days per year. Southern and southeastern Europe suffered higher frequencies of both ERT days. The occurrence of heat-related air pollution episodes rose from 7.58 to 8.49 days per year over period, primarily driven by heat-O3 events. Conversely, cold-related air pollution episodes declined from 15.61 to 9.53 days per year, with cold-PM2.5 events remaining a major threat.

Conclusion: The study identified region-specific risk thresholds to unveil spatial disparities and changes in extreme temperature events, especially when coupled with air pollution. This understanding is crucial for tailoring adaptation strategies, aiding subsequent health assessments, and implementing effective mitigation measures to safeguard public health.